It has been known for 100 years or more to store compressed gases in a gas cylinder. A conventional gas cylinder is relatively large and is not capable of being carried in comfort about the person or of being loaded into a handheld device. The gas cylinder typically stores gas at a pressure of up to 300 bar. The gas may be a permanent gas, in which case it remains in the gaseous phase, or a non-permanent gas which can be liquefied by the application of a sufficiently large pressure. The gas cylinder is closed by a shut-off valve. The valve is able to be opened manually to release the gas. Typically, although the gas is stored at a very high pressure, it is not required at such pressure. The user therefore typically fits a pressure regulator or other pressure-reducing valve to the cylinder in order to reduce the delivery pressure to a suitable value. The pressure reducing valve is therefore located downstream of the shut-off valve. Typical shut-off valves are configured so as to enable the cylinder to be filled. More recently, cylinder valves with integrated pressure regulators have been used. In all these cases the fill valve and the pressure regulator are downstream of the shut-off valve.
If the container of compressed gas is required to be fitted to a small, typically hand-held device, for example a soda-siphon or a cream whipper, a conventional thermal gas cylinder fitted with a cylinder valve is not used. Instead, the necessary gas is contained under pressure in a capsule having a water capacity of up to 100 ml. The capsule normally has a closure in the form of a pierceable seal. The capsule is engaged with a device including a hollow needle that pierces the seal in order to deliver gas. Such arrangements are generally used either when the gas concerned is a non-permanent gas stored primarily in the liquid state, or when it is desirable to release the gas as quickly as possible. In the former example, the rate of delivery of gas is limited by the rate at which the gas vaporises. The need for a downstream pressure reducing valve, for example a pressure regulator, is therefore typically reduced. In the latter example, the need to deliver the gas as quickly as possible for example, to inflatable devices such as air bags, means that a pressure-reducing valve should not be used.
There is, however, a need for a closure device for a small container of compressed gas which makes possible delivery of the gas at a reduced pressure and which avoids the use of pierceable or puncturable seals, such seals rendering the reuse of the containers sufficiently inconvenient for them normally to be thrown away.